1. Field of the Invention
The present invention relates, in general, to vehicle steering apparatus and, more particularly, to collapsible steering shaft apparatus.
2. Description of the Art
In today's vehicles, steering columns are typically designed to collapse during a collision so as to dissipate energy due to the occupant's impact with the steering wheel. Various steering columns have been devised to collapse when a certain force level is applied to the steering wheel by the occupant. Such steering columns are designed of two telescoping, tubular members. Various elements, such as frangible members, collapsible bellows, bearings, perforated sleeves, etc., are interposed between the overlapping portions of the tubular members to control the rate of collapse and to establish a predetermined force level required for the start of collapse of the steering column.
Further, in such collapsible steering apparatus, the steering shaft itself which is interconnected between the steering gear and the steering wheel must also collapse. Accordingly, such steering shafts have been formed of two separate shaft sections which are telescopingly engaged at one end. Various means have been employed to interconnect the overlapping ends of the two steering shafts to provide for simultaneous rotation of the shafts during normal use of the steering apparatus as well as to prevent any backlash or play between the two shafts. Grooves and through bores have been formed in the overlapping portions of the two shafts and filled with a moldable plastic to secure the shaft sections initially in place. The plastic is sheared by force applied to the steering wheel to enable telescoping collapse of the steering shafts. However, this technique is time consuming and requires additional manufacturing operations which add to the cost of the steering apparatus.
In a common steering shaft apparatus, the telescoping ends of the steering shaft members are formed in a so-called "TV" cross section which includes two opposed flat side walls interconnected by two arcuate side walls. The "TV" cross section extends for a short distance from the overlapping ends of the two steering shaft members before expanding into the circular cross section of the tubular, hollow steering shaft members. The "TV" cross section serves to provide longitudinal sliding telescoping movement of the two steering shaft members relative to each other during collapse of the vehicle steering apparatus and, at the same time, prevents rotation of the two steering shaft members relative to each other so that both steering shaft member rotate together as a unit when the steering wheel is turned in either direction.
However, due to the inability to maintain close tolerances between the overlapping "TV" shaped ends of the two steering shaft members, backlash and the resulting looseness between the telescopingly engaged ends of the steering shaft members results in rattles and looseness in the movement of the steering wheel. This has required the use of additional manufacturing steps, such as that described above, to securely connect the two steering shaft members together for simultaneous rotation without backlash. These additional manufacturing steps add to the cost of such steering shafts. In addition, the "TV" cross section formed on the ends of the steering shaft members requires expensive dies and equipment and a high level of expertise, all of which contribute to a high cost for the steering shaft.
Thus, it would be desirable to provide a collapsible steering shaft apparatus which overcomes the problems associated with previously devised steering shaft apparatus and methods of manufacturing the same with regard to minimizing backlash between the telescopingly engaged ends of the two collapsible steering shaft members. It would also be desirable to provide a collapsible steering shaft apparatus and method of making the same which reduces the cost of the steering shaft apparatus; while eliminating or minimizing backlash between the telescoping ends of the two collapsible steering shaft members.